Coded feed-back circuits for rail way traffic control



NOV. 7, 1944. H, A- THOMPSQN 2,362,419

CODED FEED BACK CIRCUIT FOR RAILWAY TRAFFIC CONTROL 2, HIJ Wvg/Vir Nov. 7, 1944.

CODED FEED BACK CIRCUIT FOR RAILWAY TRAFFIC CONTROL H. A. THOMPSON Filed Sept. 23, 1942 5 Sheets-Sheet 2 3l 23 El O7 i :?5 v 51% 2 "17- v e JN j (i 56 gt-r A@ `-wfri [N1/avro@ Howard/Z [Z0/@won Nov. 7, 1944. H, A `THMPSQN 2,362,4*19

CODED FEED. BACK CIRCUIT FOR RAILWAY TRAFFIC CONTROL Filed sept. 23, 1942 s she'ejcs-sheet s Patented Nov. 7, 1944 UNITED STATES PATENT l or1-lcl1-3l Howard A.. Thompson, Edgewood, Pa., assignor/4 to |The Union Switch & Signal Companywiss-` vale, Pa., a corporation of. Pennsylvania Application september 23,1942, serial No. 459,348 y1,2 claims.. (ci.4 24e-38)l My 'invention relates to coded control circuits for use in systems ofv railway' signaling and it has special reference to the employment by such circuits of the coded feed back operating principle that first was disclosed by Frank H; Nich- Olson, United States Patent No. 2,021,944 (issued November 26, 1935), and that also is shown' by numerous later patents and applications Ofcommon ownership herewith..

Generally stated, the object of my invention is to increase the utility and broaden the range of application of coded feed back control circuits of both the track and the line type;

Amore specific object is to impart to the lfeed Another object is to render bothl the feed back and 'the master code relays of such circuits highly immune to false operation by foreign f current2r that may be presentin the'- circuit conductors.

Another object is tov eliminate operating diniculties due to persistence of storage energy and/or generation of kick back energy in the conductors following each pulse of both master code and feed back energy'that is supplied thereto.

A further object is to provide improved fa'- cilities for impressing the'pulse feed back energy -upon the circuit conductors and for receiving ternating sequence and that are of relatively short individual duration; and (2)y by utilizing intervening pulses of feedback energy that also have positive Yand negative polaritiesinalternating sequence and that also are of short individual duration.

I shall describe several forms of "coded feed back control circuits which embodymy invention, and'shall then point out-the novel features' thereof in claims. These illustrative embodiments are'disclosed ifn the' accompanying drawings in which:

Fig;v A1' is a diagrammatic representation of' a track type of control circuit that incorporates the improvements of my invention and that is organized to form part of an automatic block signaling system having coded feed back appreach lighting control; y

Fig. 2 'shows' the master and feed back codes for the circuit oi Fig. 1j and' indicates' the mannerin which those codes are produced by joint operation ofthe circuit relays;

Fig. 3 illustrates modified entrance end apparatus and modied exit end apparatus for the track' circuit of'Fig. l; and

Figs. 45 and 6 show apparatus suitable for repeating both the master` andthe feed back energy pulses aroundy the insulated jointsv of a cutv section.

In the several views of the drawingsplikereference characters designate corresponding parts. Referring rst to Fig; 1, the improved control circuit organization of my invention is there dis,-

closed inassociation with a vcoded track circuit system of 'automatic block signaling for a railway track I 2 over Which'it will be assumedthat traiic moves inl the single direction indicated bythe arrow, or'from left to right lin the diagram. The protected stretch* of this track isdivided into the customary successive sections; by insulated rail joints 3"and the rails of each section form part of a track type of controlcir'- cuit which normally is capable of' transmitting energy between its two ends but which at times is rendered incapable of such transmission'.

The polar impulse frequency code. track circuit 0f Fig. 1 y In this viewof Fig. 1, reference characters II andV III respectively designate the entrance andV the exit ends of one. of these track sections.

This4 particular section is illustratively shown as medium of polar impulse code facilities which duplicatethose show-n. inv Fig. 3 of my Y issued United States Patent No. 2,282,099 earlierl re,- ferred to..

At the exit location III thoseffacilities utilize a source of positive polarity` energy T P and a source' ofl negativepolarity energyTN; a coding relay CR) having'a contact' which repeatedly picks up and releases for? thet purpose off connecting 'in`v` recurringv code. pulse. manner' the section v rails*v rst withthe positive. sourceTP and then with the negative source TN; a repeater relay CP energized over a contact 6 of device CR and having a contact 'l which shortens the pulses of both positive and negative energy that are impressed upon the section rails; a pair of code transmitters I80CT and IECT having contacts |89 and 'l5 which respectively operate at the rates of 180 and 75 times per minute; and a code detecting relay H having a contact I1 which when picked up assigns the driving circuit of coder relay CR to transmitter contact |80 and which when released transfers the driving circuit to` transmitter contact 15.

At the entrance location H the polar impulse facilities utilize a track relay TR of the polar stick code following type which has its Winding connected across the rails and which holds its contacts to the left during each positive polarity pulse of winding received energy and to the right during each negative polarity pulse of the received energy; a decoding transformer DT which receives primary current under the control of a pole changing contact-8 of the track relay; a code detecting relay H which is of the direct current 'delayed release type and which is energized from the decoding transformer secondary over a rectifying contact 9 of the track relay; a code distinguishing relay D which is energized from transformer DT through a frequency selective unit I8UDU and which picks up only when relay TR follows the 180 or high speed code; and contacts Ill-I9 through which decoding relays H-D select the indication that is displayed by Wayside signal SII.

In the form shown, this signal is of the wellknown color light type. Its clear lamp G is lighted when the relays I-I-D are both picked up; its approach lamp 'Y is lighted when relay I-I is picked up at a time that relay D is released; and its stop lamp R is lighted whenever relay H is released.

In the polar impulse track circuit combination of Fig. 1, the earlier described exit end or location III apparatus operates in the following manner. With the track section in advance of location III vacant, contact II of relay H assigns coding relay CRs driving circuit to transmitter contact IBI) and thus causes the relays` contacts .5 6 to operate at the high speed or 180 code rate.

Each pick-up or front closure of contact 5 produces a positive period in the master code energy pattern that is represented in Fig. 2. During the continuance of the energy pulse which denes that period, the positive source TP maintains rail I positive with respect to rail 2. This is done over a connection extending from the positive terminal of source TP through front contact 5 of device CR, conductor II, the track rails I and 2, conductor I3, a current limiting impedance I2, and contact 'I of device CP in its right or reverse position (shown dotted) back to the negative terminal of source TP.

Upon eachv release of the coding contact 5 there is produced a negative period in the master code energy pattern of Fig. 2. During the continuance of the energy pulse which defines that period the negative source TN maintains As the specification of my issued United States Patent No. 2,282,099 more fully explains, the repeater relay CP is a code following device of the "polar stick or magnetically toggled type. Flow of energy over vdevice CRs front contact 6 through the left portion of relay CPs winding moves contact 'I to the left or normal position, while flow of energy over CRs back contact 6 through the right portion ci the relay CPs winding shifts `contact 'I to the right or reverse position. Once, moreover, contact 'I reaches either `of these two positions, it there remains continuously until the Winding of relay CR receives energy of the opposing polarity. i

As my issued United States Patent No. 2,282,- 099 further explains: (l) each back contact closure by coder relay CR thus causes the repeater y device CP to shift-its contact 'I from the left or normal to the right or reverse position; and (2) each front contact closure lby device CR. thus causes relay CP to shift contact 'I yfrom its right or reverse position back to the left or normal position. Each of these shifts is accompanied by a short delay during which each of the rail supply circuits earlier traced is completed. In consequence, the recurring pulses of positive polarity energy supplied from source TP are rendered much shorter than the recurring code periods which those pulses define and the intervening pulses of negative polarity energy `from source TN likewise are rendered much shorter than the intervening code periods which those .pulses dene.

This will become more apparent upon reference to Fig. 2 wherein: (l) the elevated portions of the CR pattern designate picked up conditions of contacts 5 6, while the depressed portions of the same pattern designate released conditionsv of those contacts; and (2) the elevated portions of the CP pattern designate a normal or left closure of Contact l, while the depressed portions of that pattern designate a reverse or right closure of the same contact.

If, for example, contacts 5-6 of device CR reach their picked up position at point a, then the repeater relay contact 'l will begin moving from its right to its left position at the slightly later point b, Likewise, if contacts 5-6 reach their-released position at point c, then repeater relay contact 'I will begin movement from its left to its right position at the slightly later point d.

Each of the positive pulses of master code energy supplied from source TP will, therefore, be of the relatively short duration designated at a-b in Fig. 2, and each of the negative pulses supplied from trackway source TN will have a corresponding shortness designated by c-d in Fig. 2. As compared with the total length a-c and c--e of the positive and negative code periods which the just named pulses respectively dena'the duration of rail energy application will be seen to be relatively short.

In being transmitted over the section rails to entrance location II, each positive polarity pulse ofV master code energy causes the track relay TR to move its contacts to the left or normal position and each negative polarity energy pulse causes the relay to shift the contacts to the right or reverse position. Each of these shifts takes place rapidly and requires only a short application of energy to the relay winding.

This action is shown by the TR portion of Fig. 2. There the elevated portionsv of the pattern designate left or normal closures of the track relay contacts, while the depressed portions of the pattern designate right or reverse contact closures. From Fig. 2 it will be seen that operation of the track relay TR is exactly the same as were each of the positive pulses of master code energy to be prolonged for the full duration of the positive code periods and. each of the negative pulses to be prolonged for the full duration of the negative code periods.

In the entrance end organization shown, such a code following operation by the track relay TR causes the detector relay H to hold its contacts continuously picked up regardless of whether that operation be at the high speed or 180 code rate or at the low speed or 75 code rate. In either event, the Winding of relay H receives (from source terminals plus and minus and through transformer DT) code frequency pulses of energizing current which hold contacts l'l-IS picked up.

In the case of code distinguishing relay D, however, pick-up occurs only when the track relay TR follows code at the 180 or high speed rate. And finally, stoppage of relay TRs code following operation causes relays H and D both to release.

From the foregoing description of the polar impulse coded track circuit apparatus of Fig. 1, it is apparent that a three indication automatic block signaling system may be provided by equipping each of a plurality of consecutive track sections with this Fig. 1 apparatus and arranging that the entrance end relay H of each section determine (by means of contact l1 as shown at location III) the rate of pulse recurrence of the polarized master code energy Ythat is supplied to the exit end of the rear adjoining section.

Each train passing through such a signaled stretch of track sets up its own following protection in the three indication automatic block manner which my issued United States Patent No. 2,282,099 explains in detail.

Approach control apparatus of Fig. 1 Coded track circuits of the "polar impulse type just described provide a most desirable form" of block signal control and When organized into a complete frequency code system, they offer a number of important advantages. As the specincation of my United States Patent No. 2,082,099 more fully sets forth, these include a lowering of the power requirements of the track circuits, a raising of the immunity to false operation by foreign currents, an elimination of operating difculties due to storage energy persistence, a lowering of code distortion effects, and an improvement in shunting sensitivity. All of these advantages are, of course, in addition to the obvious elimination of all signal control line wires.

In many instances it is further desirable to approach energize the wayside signals SII, SIII, etc., and certain other traliic governing devices of the complete system. To meet this need, I have evolved the non-line-wire approach control combination which in one preferred form is further shown by the diagram of Fig. 1.

This combination utilizes the coded feed back operating principle of the earlier named Nicholson United States Patent No. 2,021,944, and the Fig. l form thereof requires that the polar impulse track circuit combination earlier described be supplemented by certain apparatus which will now be named.

At Fig. 1s exit location III, this supplemental apparatus includes: (1) an approach relay AR having a contact 2| which keeps wayside signal- SIII4 deenergized at. all times except when a train approaches the signal location over the rails of section II--III; (2) a detector relay KR which, controls the energization of relay AR through the medium of contacts 23-24 and an interposed transformer AT; and (3) circuits over which the winding of relay KR is connected in energy receiving relation with the section rails I-2 during the oif portions of the master codes positive and negative periods.

At Fig. ls entrance location II, the supplemental apparatus includes: (1) a source of positive polarity feed back energy KP and a source` of negative polarity feed back energy KN; (2) a repeater device RP for track relay TR which is energized over that relays Contact 25;` and (3) circuits including contacts 26-21 of device RP and Contact 28 of device TR over which sources KP' and KN are selectively connected with the section rails l-2 during the olf portions of the master code positive and negative periods.

Entrance end relayV RP has response characteristics similar to those earlier explained for the exit end repeater CP. Flow of current over device TRS left or normal contact 25 through the left portion of relay RPs winding causes contacts 25--21 to move to their left or normal such shift is accompanied by a short period of response delay. During lthis delay, one or the other of the feed back sources KP-KN is connected with the section rails and as a result i those rails are supplied with intervening pulses of feed back energy that have positive and negative polarities in alternating sequence and that are of short individual duration.

The character of these feed back energy pulses will best be understood upon reference to Fig. 2. From that ligure it will be seen that each positive pulse of master code energy is followed by a negative pulse of feed back energy and that each negative pulse of master code energy is followed by a positive pulse of feed back energy.

The manner in which these feed back pulses are supplied will now be explained. Under vacant conditions of track section II-III, the track relay TR moves` its contacts 25-28 :from their left to their right and from their right to their left positions repeatedly and in respective Step with the pick-ups and releases of coder relay CRs contacts 5--6 at the section exit. At times this contact movement takes place at the high speed or code rate and at other times at the low speed or 75 code rate.

In either case, each left positioning of rela-y TRs contacts 25--28 is followed after a brief time'interval by a transfer of repeater device RPs contacts 26-21 from their right to their left positions. Similarly, each movement of the track relay TRs contacts 25-28 to their right positioning is followed after a brief interval by a transfer of repeater device RPs contacts 26-27 from their left position to their right position. l

Again referring to Fig. 2, if the track relay contacts reach the left positions at instant lc, then the repeater relay contacts will leave their right positions at the somewhat later instant l;

if -the track relay contacts'return to their right positions at instant m, th'en the repeater relay.

contacts will leave their left positions at the somewhat later instant n; and so on.

Upon each left positioning of the track relay contacts. the section rails are supplied with a negative polarity pulse of feed back energy. This supply is over a circuit which extends from the positive terminal of feed back source KN through right contact 26 of device RP, conductor 30, track rails 2 and I, conductor 3I, vthe winding of relay TR, conductor 32, left contact 28 of device TR and conductor 33 back to the nega-r tive terminal of source KN.

This negative feed back supply continues for the time (see Ic-Z of Fig. 2) required for the repeater device RP to open its right contact. As shown in Fig. 2, this time is relatively short. The direction of feed back current flow through the winding of track relay TR is, moreover, such as to continue contacts 25-28 in their left positions. v

- Upon each right positioning of the track relay contacts by a pulse of negative polarity master code energy, the track rails are supplied with a positive polarity pulse of feed back energy.'

This supply is over a circuit extending from the positive terminal of source KP `through right contact 28 of device TR, conductor 32, the wind-v ration illustrated. During that pulsemoreover,

the flow of feed back current through the wind-4 ing of track relay TR is in the direction which urges that relays contacts 25-28 more rmly into their newly established right positions.

In the manner just stated, therefore, each response of the track relay TRto a positive pulse of master code energy causes the rails to be supplied with a negative pulse of feed back energy, and each response of the track relay to a negative pulse of master code energy causes the rails to be supplied with a positive pulse of feed back energy. l

' For assuring proper connection of the track relay with the section rails during each reception of a master code energy pulse, use is made of the repeater device RPs second contact 2l. Through the medium of this contact and the track relay's contact 28, there is established between conductors 30 and 32 a current path over which the track relay winding is energized by each positive polarity pulse and by each negative polarity pulse of master code current that is received at the entrance location II.

`Referring again to Fig. 2, it will be seen? (l) that following each rail-supplied pulse of negative polarity feed back energy, contacts 21-28 of relays RP-TRboth occupy their left positions;` and (2) following each positive pulse of rail supplied feed back energy, contacts 21-28 of devices RP-TR both occupy their right-positions.

. Under the condition irst stated, there isv completed for the winding of track relay TR a master code energizing path `that extends from section rail2, through vconductor `3f), vleft contact 21 of device RP, conductors 35 and 33, the left contact 28 of device TR, conductor 32, the winding of relay TR and conductor 3l back to section rail I. It is over this path that a succeeding negative polarity pulse of master code current energizes the track relay TR.

Under the conditions second stated above, there is set up for relay TR a master code energizing pathwhich extends from section rail I, through conductor 3l, the winding of relay TR, conductor 32, right contact 28 of 'device TR, conductor 36, right contact 21 of repeater RP, and conductor 30 back to rail 2. Itis over this path that a succeeding pulse of positive polarity master code current energizes the track relay TR.

Once established, moreover, each of the connections just traced remains intact until the track relay TR shifts its `contacts in response to the received master code energy. When that happens, the connection is, of course, broken at contact 26 and the Winding of relay TR then becomes momentarily disconnected from the section rails. The track relay energization which preceded that disconnection is, however, sufficient to complete the transfer of contact position and in consequence, relay TR follows code in the same manner as were its circuit conductors 33 and 32 to be continuously joined together.

At the exit end IlIof the Fig. 1 track section, the just described feed back energy pulses are impressed upon the winding of the detector relay KR in a manner which will now be explained.

This detector relay KR is a code following device of the polar biased type and it responds as noted below. In the absence of current iiow through the relay winding,` contacts 23-24 occupy the released position shown dotted; flow of current through the relay winding in th'e direction of from left to right (see the small arrow) picks contacts 23-24 up to the position shown in full lines; and iiow of winding current in the opposite direction of from right to left urges contacts 23-24 downwardly into their released position.

Relay KRs winding is connected with the track rails over conductors I3-M, pole-changing contacts 39--40 of the master coder relay CR, contacts 50 and 5 of devices CP and CR, and conductors II and I3. Over this connection each pulse of feed back energy that is received from entrance sources'KP-KN picks up relay KRs contacts while each pulse of master code energy that is supplied from exit sources TP-TN keeps those contacts released.

The stated pick-up of relay KRs contacts is effected by received feed back energy of both the positive and the negative polarity. This is due to the pole-changing action of coder relay CRs contacts 39-40. Because ofthat action all received feed back pulses of either polarity flow current through relay KRs winding in the arrowindicated direction of from left to right.

Looking rst at the positive feed back pulses, it has already been seen (from Fig. 2) that each such pulse makes rail I positive with respect to rail 2 and is accompanied by a closure of coder relay CRs back contacts plus a closure of repeater relay CPs right or reverse contacts. In appearing between the rails at the exit location III such positive feed back potential thus picks up relay KR over a path extending from rail I through conductor II, device CRs back contact 5, conductor 54device CPs right contact 50, conductor 52,A device CRs back contact 39, conductor I4, the

winding of relay KR, conductor I5, device CRs back contact 4K3', and conductor I3 back to rail 2.

Looking next at the negative feed back pulses, it has already been seen (also from Fig. 2)v that each such' pulse makes rail 2 `positive with respect torail I and is accompanied by a closure of coder relayv CRs front contacts. plus a closure of repeaterrelay CPs vlefty or normal contacts. In appearing between the rails at location III such negative'feed` back potentialv thus picksup the detector `relayKR over a .path extending from rail 2 throughv conductor I3, device CRs lfront' contact 39, conductor I 4, the windingl of` relay KR, conductor I5, device CRsfront contact Iii), conductor' 52', device CPs left Contact 50, conductor '53, device CRS front contact 5, and conductor I I back to rail I.

As long therefore', 'as Fig. ls track section II-III remains vacant: (l) recurring pulses of positive and vnegative polarity feed back energy are lreceived from the'rails at the location Aof relay caused to lpick up its contacts 234-24 and at the end` of eachof tnosepulses itis allowed to` release these. contacts; and (3) in thatv way the detector relay KR'is operated incoclefollowing manner by feed hackl pulses which are transmitted thereto from entrance sources K13-KN.

Nor is this .action in any way interfered with by the pulses of master code energy with which the. rails are supplied by sources TP-TN at the detectorrelay location. From` Fig. 2 itis seen that each.k of these pulses of master code energy has a polarity which is opposite to that ofthe feed back-pulse which immediatelyfollows it. That is,A each positivevpulse of feed back energy is immediately preceded by a negative pulse of master code energy-while each negative pulse of feedback energy is immediately` preceded by a positive pulse of master code energy.

During, therefore, 'thel cooleperiods in vwhich the detector-relay K R ispicked up by positive feed back energyfthef-master energy potential earlier impressed thereon is of negative polarity and serves only to urge relayKRs contacts more rmly into their releasedv positions. f Likewise,

- KR; 2.) .that relay is` by each of those pulses `feed back. approach control facilities will have duringthe code periods in which the detector rev lay KR is picked upby a negative'feed back pulse, themaster energy potential earlier impressed thereon is of positive polarity and serves onlyl to urge relay KRS contacts more firmly. into their released positions. f l

The detector relay KR is, accordingly, responsive to and only :to feedback energy that is received over therails from. entrance sources KP-'KN. Because of its A;;"polar-biased characteristicsthat relay KR cannot be picked up by master code energy which further .is impressed thereon by exit sources ,TP--TN. Under occupied section conditionsytherefore, the master code energy. which then.'` continues to be impressed` on relay KR" can-never move the contacts of that relayoutof their released position.

Codefollowingl l operation on the part of detector relay KR thus can occur only when Fig. ls section II'III i's vacant. Such operation results in the approach relay AR receiving recurring pulses of energizing' current which hold contact 2i continuously Vpicked up. Such approach relay energy isderived from source terminals plus and.minus,"and is transmitted to the relay Winding over pole changing contact 23, the

KRs contacten-24 remain in one'position continuously, energy transmission through transformer AT' then ceases and the approach relay AR releases its contact 2|. By such release, lighting. current is supplied to wayside signal SITI; Optionally, of course, any' other function or' approach control might be performed by contact 2|.

The mode'cf operation of my improved coded becomemore or less apparent from the foregoing description of the entrance and exit end apparatus which. the Fig. 1 track circuit utilizes. At all times, the continuously operating coding and repeater devices CR-CP connect the section rails l and 2 alternatelywith the positive and negative exit end sources 'I'P and TN and therebyv` produce a master code having the polar impulse character which the upper portion of Fig. 2 shows.

In being received at the section entrance, the energy pulses of this master code operate track relay TR in conventional code following manner. Aided by repeater device RP, that relay alternately connects the section rails I and 2 with the negative and the positive polarity sources KN and KP and thereby produces a feed back code having the polar impulse character that is represented by the lower portion of Fig. 2.

Inbeing received at the exit location III, the energy pulses of this feed back code operate detector relay KR in the codefollowing manner earlier described. As a result of such operation, the approach relay AR holds contact 2I continuously picked upy and thereby maintains, wayside signal SIII normally deenergized. Such deenergization continues as long as the track section II-III remains vacant.

In the event now that a train comes into the section, the usual shunting action of its wheels and axles cuts off transmission of master code energyto the entrance end track relay TR and alsov discontinues transmission of feed back energy to4 the exit end detector relay KR.. In

consequence, relay KR ceases to pick up and release contacts 23-24 but it allows those contacts to. remain continuously released.

As a result, transformer AT now discontinues all transmission of pick-.up energy to relay KR and causes that. relay to release contact `2|. That release, of course,v connects wayside signal SIII with its lighting source and thereby causes that signal to display the particular indication which is selected by decoding equipment I-I-D.

This release of the approach relay -AR continues until the train moves out of section II-III When that happens, ymaster code energy is again transmitted to entrance end track relay TR, the section rails are once more supplied With feed back pulses, and by those pulses the exitend detectorrelay KR is again operated in code following manner. By that operationgthedetector relay contacts 23-24 restore the supply of pickup current to the approach relay AR. That relay, inv turn, again picks up contact 2l and thereby restores the Wayside signal SIII to its normally inactive condition.

Direct current track circuits of the coded feed back type frequently have to safeguard their feed back energized relays against false operation due to inductive kick back energy which may bey generated in the track rails when those rails 'are shunted by a train. In the track cir` cuit of Fig. 1 such so-generatedkick back energy appears in rails I-2 at the end of each on period pulse of unidirectional current which master code sources TP-TN impress upon those rails over contacts 5 and 'I of coding devices CR and CP.

Direct current track circuits employing detector relays of the type shown at KR in Fig. 1 can experience serious operating difficulties due to such kick back energy and one early proposal to overcome such difliculties forms the subject of assignees United States Patent No. 2,286,002 which issued to Frank H. Nicholson on June 9, 1942.

As the specification of that patent sets forth in considerable detail, kick bac energy of the type here considered results from the inductance of the track circuit plus the conductance of the rail-to-rail ballast and its effect is to continue for a short interval after each disconnection' of direct current sources TP-TN from the section rails the flow of current in those rails in the same direction as the so-disconnected source had established.

When, therefore, the rails of Fig II--III are shunted by a train, each on period pulse of master code current which sources TP-TN impress upon those rails may be followed by a kick back energy pulse which though relatively short still is long enough to overlap the early portion of the succeeding olf code period (see Fig. 2). Current due to these overlapping pulses thus may reach relay KR over 1s section conductors I I and I3, contacts 5, 50, 39-40 of devices CR-'CP, and conductors I4-I5.

If of sufcient magnitude such off" period kick back current may falsely cause relay KR to follow code even though the approach relay AR controlled thereby should stay released until the train has cleared the section.

In order to guard against such false operation of detector relay KR the exit end apparatus of Fig. 1 may be supplemented by a reactor 55. Preferably this reactor is organized in the saine basic manner as my copending application for Letters Patent of the United States Serial No. 455,170 discloses and claims, and it then serves to keep relay KRs winding connected with the section rails during the master code off periods when coding devices CR and CP are shifting Ytheir contacts 5 and 50.

Such connection enables advantage to be taken of the inductive characteristics of relay KRs winding plus those of the reactor 55. The eifect of such characteristics is to generate a local kick back voltage at the end of each passage of unidirectional current through the reactor and relay Winding. That effect is, of course, produced by the collapse of magnetic flux which accompanies each disconnection of the named elements from their D.C. energizing source.

By the added reactor 55 there is established for relay KRs winding a path over which each pulse of master code energy from eXit sources TP and TN flows current through the Winding of KR in the direction of from right to left. In the case of each positive pulse, such flow is from the positive terminal of source TP over device CRs front contact 5. through reactor 55, device CRs front contact 48, conductor I5, the winding of relay KR, conductor Irl, device CRs front contact'39, conductor I3, impedance I2 and device CPs right contact 'I back to the negative terminal of source TP; in case of each negative pulse such ow is from the positive terminal of source TN, through device CPs left contact 'I,

impedance I2, conductor I3, device CRs back contact 40, conductor I5, the winding of relay KR, conductor I4, device CRs back contact 39, reactor 55, and device CRs back contact 5 back to the negative terminal of source TN.

As earlier explained, such right-to-left current ow through relay KRs winding is ineffective for picking up relay KR and thus it does not interfere with the desired code following response of that relay to the feed back code pulses which are applied thereto under vacant section conditions. It does, however, render the relay immune to false pick-up by master code kick back energy which may be applied thereto following each disconnection of exit sources TP--TN from the section rails.

Upon each of these disconnections: (1) the section rails I--Z tend to flow' through the Winding of relay KR a master code kick back current in the direction of from left to right; and (2) the energy of self-inductance in relay KRs winding plus that in reactor 55 tends to continue the flow therethrough of current in the opposite or right-to -left direction.

These currents directly oppose each other and by choosing the magnitude of the windings plus reactors kick back current to slightly exceed that generated in the rails, relay KR is effectively held released following each disconnection of master code sources TP-TN from the shunted rails.

In practice, reactor 55 may take the form of an adjustable element which is set at such a value as to produce the relation just expressed. Should relay KRs Winding itself be capable of producing all of the counter inductive effect that is needed, then the reactor 55 may be replaced by a resistor (not shown) or other impedance. Most code following relays of commercial design are, however, found to require some counter inductive supplement when employed as is device KR at location III of Fig. 1 and for this reason use of the represented reactor for element 55 ordinarily will be preferred.

At Fig. ls entrance location II no kick back neutralizing reactor is provided for the reason that none is there needed. In preventing track relay TR from falsely being picked up by kick back energy that following each disconnection thereof from feed back sources KP-e-KN may be present in the rails, this location II organization of Fig. 1 utilizes the expedients of assigneesl United States Patent No. 2,286,002 to Nicholson.

Trackway current originating in each of sources KP--KN passes in series through the winding of relay TR in such direction as to hold that relays contacts in the position to which they were biased by the pulse of master code energy last received from exit end source TP or TN. As any resulting kick back current in the section rails flows in the same direction through the relay winding it cannot produce false relay operation and hence no neutralizing reactor is needed for the relay TR of Fig. l.

The modified combination of Fig. 3

The just described coded feed back track circuit organization of Fig. 1 incorporates only one of several possible structural arrangements which may be utilized to perform the explained functions. In Fig. 3, I have represented a generally equivalent track circuit combination wherein both the entrance end apparatus and `the exit Zend -zapparatus :is vmodified :als to tain of its details. f

As in the organization ,of Fig. 11, `the complete combination of Fig. :3 utilizes the :basic polar impulse track circuit elements earlier descr'ibed y:as being identified with my issued United States Patent No.'2,282;099. These elements comprise: (1) 'at the section,.eXitIIIf-coder and. Repeater TP and TN of -master code trackway energy,

"and rail supply circuits in which lthese sources lare included; and (2) .at the vsection'entrance plete track circuit combi-nationcf Fig. 3 further i kuses feed fback elements AA.which comprise: 1,(19

.at the sec-tion entrance IIe-.a .repeater devicelRP .-for track relay TB., 4positive:and negative sources rail-supply circuits in which these Sources` ,are .selectively included; .and .(2) tat the .section exit III-an approach relay which :governs the energiza-tion -of signal :SUL 1a detector :relay KRI which control-s jthe energization of relay AR, :and circuits over which relay .-K-Ri Areceives feed hack energy -from the section rails.

At Figs. 3s exit end III, the coder and repeater relays CR-CP .are broadly .equivalent lto zthe similarly' designatedv elements of Fig. ,1. The

same is true of; master 'energy sources l and the circuits overwhich devices CR-.CPselectively connectthese sources in .energy .supplying relation with the. section rails' I-z y;

At Fig. 3s .entranceend 1I., the reed :back sources KP-KNalso ,have a close .correspondence to the .similarly designated elements of Fig. 1 but differ in the mannerin Lwhich r.they iareconnected with the section rails 1|-,2.

Whereas in-.ligxA 1 these .sourcesgsupply yfeed back -current to the rai-ls over .-a ser-ies connection with the wind-ing o f track relay TR., in Fig. 3 the feed back supply circuits are connected in parallel with the track relay winding and thus impress their energy upon .the track rails in `.a somewhat more fdirect manner. The supply connection ,for both sources maycptional-lyinciudea current limiting impedance'43. 1

A further difference between the Fig.. 3 land the Fig. l1 organizations Vis that -eac-h reception by the .track relay .of a positive pulse :of master code energy `is followed -bya connection with .the

`section rails of the `positive feed back source KP .instead of the negative source `KN yand that each reception vby .the track .relay TR of a neg- :ative pulse ofJmaster code energy is followed by .a .connection of the .track railswith :the negative vrelays CR and CP-p,0sitive and negative fsources leftor normal position. When that happens, .the pulse of positive feed back energy is interrupted. During its continuance, however, this pulse ener.- lgizes the track relay TR in a `direction tending ltoho'ld contacts `25`28 in their just established Vnormal or left position. f

Each of the earlier named negative feed back :energy supply connections is established upon movement .of track` relay TRs contacts 25-28 to their right or reverse position. Such movement completes -for the section rails a negative :feed

.back supply circuit which extends yfrom theA posivtive terminal of source .KN vthrough normal contact :2.6 of repeater RP, in'npedanceA l113, .conductorl 320, .track rails v2 .and 1, conductors' 3i .and 45, n

and the reverse Contact 28 vof lrelay TR hack to the negative terminal of'source :Once established, this negative supply connection continues until relay' RP. shifts its k'contacts away from .fthe left orreverseposition and thereby .disconnects :source KNfroni the rai-ls. During the continuance of, each so-supplied pulse of negativefeed back'fenergy, `the track vrelay is energized in the direction whichholds its contacts 25--28 in their newly established right or `reverse position. y

lthisiunicue correlation of the feed .back and :master code energy polarities the entrance end `Feed 'back supply facilities 'of 3 function inv :the desired manner without interfering with the master icodeoperation of the code following track f relay TR. Such lack .of interference, quite obviously, results only when each positive pulse of `received master code `energy is immediately iolflowed Tby a positive pulse of 4supplied feed back energy, :and leach negati-ve pulse of received mas- .ter .code -enerevis followed by `a negative pulse Eof supplied Vfeed black energy.

2t-eed back source instead of the positive .source .KPas in Fig. .1.

Each y.of these positive feed :back connections results from a positioning of the track relay contacts 2.5-2.8 to theleft; There is then ccmpleted for the .section `rails ja feed .backfsnpply .circuit that `extends from the positive terminal -of .source .KP through conductor 44, left .contact 28 :of device conductors 115 and ,31, track rails Ll and 2, conductor 30, impedance 43, right `contact 25 .of device RP, Yand conductor 46 bazck to the negative terminal Yof source `Once completed, connection remains in- Ln the Fig. l organization, wherein the feed back energy flows serially through the track relay winding, a [correspond-ing lack .of interferencey is achieved :by use of the inverted polarity master .code .and feed flo-ack Ienergy relation lwhich Fig. 2 represents. When using the Aseries track relay .connection `of Fig. 1, .that inverted relation is yessential :arr-.d the coinciding lmaster code, and feed .hack polarity r-relatiorrof Fig. 3 cannot directly be substituted therefor. l

In this coinciding polarity organization of Fig. .3 .it is sometimes desirable to supplement the' basic'entrance Iend Ecombination `just described .by `a reactor `5t organized as per my .-copendi-ng applicati-on torLett'ers Patent .of the United StatesY `Such ra reactor keeps relay to inductive kickback `energy thatmay'be presf .ent in .the track rails `immediately Afollowing `the `iced 4.back pulse ends. Y

.As `lllrev-iousl-y explained relative to Fig. lis exit :end reactori, such kick black energy results .from .the inductance of the track 'circuit vlplus the to .he :present in .therails of a'shunted -track section at the end of each direct current energy ,puise :that is impressed thereon; and when-so gen .erated its effect is,y to .continue for a .short time after eachdisconnection .of .the D.C. source from ,the rai-ls .the iiow of current in the same direction .asv/.as established by that source.

If .in the entrance end Iorg-anization of Fig. .3

tact until repeater RP shifts its contact to Athe v,ill such ,fkick hack .velleit-Y pe'lSiS'fS after Gfh diiSfconnection of feed back sources KP and KN from the section rails it will, therefore, ow current through relay TR in such a direction as falsely to shift that relays contacts from the position established by the immediately preceding pulse of master code energy that was received over the rails. Under operating `conditions of Fig. 3s track section II-III such false contact shifting is objectionable and the purpose of added reactor 56 is to make it impossible.

By that reactor 56 there is established for relay TRs winding a connection through`which each rail-applied pulse of feed back energy ows unidirectional current through that winding. The direction of this flow is: (l) from left to right in the case of each feed back pulse from positive source KP (which makes rail positive with respect to rail 2) and (2) from right to left in the case of each feed back pulse from negative source KN (which makes rail 2 positive with respect to rail In both instances the path-of Iiow for this relay Winding current includes contacts 26 and 26 of devices RP and TR, impedance 43, and reactor 56.

In each instance, moreover, this feed back current passes through relay TRs Winding in the same direction as did the master code trackway current to,which relay TR responded immediately before connecting Fig` 3s source (KP or KN) of feed back current to the rails. This is because each of Fig. 3s positive pulses of supplied feed back energy (rail positive with respect to rail 2) is preceded by a positive pulse of received master code energy and each of Fig. 3s negative pulses of supplied feed back energy (rail 2 positive with respect to rail l) is preceded by a negative pulse of received master code energy. In Fig. 3, there-y fore, the desired code following response of track relay TR to received master code energy is in no way interfered with by reactor 56.

In rendering track relay TR immune to false operation by rail kick back energy, that reactor 56 makes use of the before described unidirectional current which flows through the inductive turns of the reactor and of relay TRs winding during each and every pulse of feed back energy with which the rails are supplied by sources KIEL-KN. Such current builds up magnetic iiux around those turns and in being interrupted at each feed back pulse end the resulting collapse of that flux generates a local kick back current in the winding and reactor. By that local current, relay TR is prevented from shifting its contacts in response to trackway kick back energy.

Thus, upon each disconnection of Fig. 3s positive source KP from the section rails |-22 (l) those rails tend to flow through the winding of relay TR a feed back energy kick back current in the direction of from right to left; and (2) the energy of self-inductance in relay TRs winding plus that in reactor 56 tends t'o continue the flow therethrough of current in the opposite or left to right direction. These currents directly oppose each other and by choosing the windings plus reactors kick back current to slightly exceed that generated in the rails relay TR will hold its contacts to the left, under the conditions stated.

Similarly, upon each disconnection of the negative source KN from Fig. 3s rails: (l) those rails tend to flow through the winding of relay TR a feed back energy kick back current in the direction of from left to right; and (2) the energy of self-inductance in relay TRs winding plus that in reactor 56 tendsvto continue the flow therethrough of current in the opposite or right to left direction. The latter current overcomes the former and thus holds relay TRs contacts to the right, under the conditions stated.

Should relay TRs Winding itself be capable of producing all of the counterinductive effect that is needed for the above, then the added reactor 56 may be replaced by a resistor (not shown).

In order that the operating sensitivity of Fig. 3s code following track relay TR will not be impaired by this added reactor 56 provision is made for by-passing that reactor whenever a master code energy pulse is being received. Such bypassing is effected by contacts 21-28 of devices RP and TR. Those contacts establish around reactor 56 a current -path over which relay TRs winding receives each positive polarity pulse and each negative polarity pulse of master code energy that reaches location II.

This reception takes place in the following manner. Immediately after each rail-supplied pulse of positive polarity feed back energy, contacts 21-28 of relays RP-TR both occupy their left or normal positions and immediately after each rail-supplied pulse of negative polarity feed back energy contacts 21-28 of devices RP-TR both occupy their right or reversed positions. Under the condition last stated there is completed for the winding of relay 'I'R a master code energizing path which extends from section rail through conductors 3| and 56, relay TRs right contact 28, conductor 6|, device RPs right contact 21,- conductor 61, the winding of relay TR and conductor 30 back to section rail 2. It is over this path that a succeeding positive polarity pulse of master code energizes the track relay TR` Under the condition rst stated above there is completed for the winding of relay TR a master code energizing path which extends from section rail 2 through conductor 30, the winding of relay `TR, conductor 61, device RPs left contact 21,

conductors 14 and 44, relay TRs left contact 28, and conductors 45 and 3| back to section rail I. It is over this path that a succeeding pulse of negative polarity master code energy flows current through the winding of track relay TR.

Once established, moreover, each of the connections just traced remains intact until the track relay TR shifts its contacts in response to received master code energy. When that happens the connection is, of course, broken at contact 28 and the winding of relay TR then becomes momentarily connected with the section rails through reactor 56. The track relay energization which preceded that contact shift is, however, sucient to complete the transfer of contact position and in consequence relay TR follows code in the same manner as were reactor 56 not included in its circuit conductor 3|.

Looking next at the exit or location III feed back facilities of Fig. 3, it will be seen that they too are basically similar to the corresponding facilities of Fig, 1 but differ therefrom with respect to the circuit over which the detector relay KR| is connected with the section rails |-2.

As in Fig. 1, this detector relay is a code vfollowing device of the polar biased type and by it the slow release direct current approach relay AR is controlled in precisely the same manner as in Fig. 1. Contact 2| of Fig. 3s relay AR is, therefore, held continuously picked up as long as the detector relay KR| follows code, and releases only when contacts 23-24 of the detector relay remain in one of their two positions continuously.

back pulse of opposing polarity (see Fig. 2), the Fig. 3 combination is so set up that each received master .energy pulse is followed by a feed back pulse of the same polarity.

' vAt Fig. 3s exit location III, therefore, each master energy pulse that is supplied under Vacant section conditions is immediately preceded by a received feed back pulse of the opposite polarity, and connections of Fig. 3s detector relay (KRI) winding with the rails are so set up that current due to each of those received feed back pulses flows through that winding in the arrow-indicated direction of from left to right.

Relayv KRls winding is also energized during each pulse of master code energy that exit end sources TP-TN supply to the rails. As has been seen, however, such energization flows Winding current in the direction of from right to left and hence is ineffective forpicking up relay KRI. Kick back energy which may follow each disconnection of sources TCP-TN from the rails would, of course, reverse this direction of ow were the connection of relay KRI s winding with the rails to remain unchanged.

At the end of each master code pulse, however, that connection is reversed by contacts 5-50- 48-,49 of devices CR-CP and any current due to rail kick back energy `that reaches relay KRls winding thus also fiows therethrough in theright to left direction and hence also is ineffective for producing relay pick-up.

In consequence, the track circuit of Fig. 3 is inherently immune to false operation of its exit end detector relay KRI by rail kick back energy and hence no reactor corresponding to Fig. 1 element 55 need be used therewith.

, Cut section facilities of Fig. 4

In certain instances it may be desirable to subdivide the main signal block II-III of the Figs. 1-3 systems into two or more track sections. Typically, such subdivisions will be occasioned byrequirements of excessive block length, highway crossing control or other equally well-known reasons.

In the event of such subdivision, means mustv be provided for repeating into the rails of each rear section the master code energy pulses that are supplied to the rails of each forward section and for repeating into the rails of each forward section the feed back energy pulses that are supplied to the rails of the rear section. In a system of the type shown by Figs. 1 and 3,

moreover, the repeated pulses must have not only the same timing but must also vbe of alternately opposite polarity.

Facilities vfor performing such code repeating functions are illustrated in Fig. 4. There a block subdividing or cut section location IIa is shown as being occasioned by insulated joints 3 which are interposed between the entrance and exit locations of a signal block which has the character represented at II-III in each of Figs- 1 and 3. Operated by the positive polarity master code energy that is received from the forward section rails I2 is a code following track relay TRP; operated by the negative polarity master code energy that is received from the forward section rails is a second code following track relay TRN; operated by the positive polarity feed back energy that is received from the rear section rails Ia-Zais a third code following track relay KRP; and operated by the negative polarity feed back energy that is received from the rear section rails is a fourth code following track relay KRN.

Controlled by a coding contact 51 of relay TRP is a positive source TP of master code energy for the rear section rails; controlled by a coding contact 58 of relay TRN is a negative source TN of master code energy for the rear section rails; controlled by a coding contact 59 of relay KRP is a positive source KP of feed back energy for the forward section rails; and controlled by a coding contact B9 of relay KRN is a negative polarity source of feed back energy for the forward section rails.

Each pulse of positive polarity master code energy that is received from the-forward section rails at location IIa picks up relay TRP over a circuit extending from rail I through conductor E2, back contact 59 of relay KRP, back contact 69 of device KRN, conductor 63, a back contact S4 of device TRN, conductory 65, the winding of relay TRP and conductor 66 back to rail 2. During each of these pick-ups, relay TRPs contact 51 causes source TP to supply the rear section rails with a pulse of positive polarity master code energy. The supply circuit extends from the positive terminal of source TP through a current limiting impedance B8, conductor 69, the rear section rails ii-2a, conductor 19, front contact 51 of relay TRP and conductor 1l back to the negative terminal of source TP.

Each forward section pulse of negative polarity master code energy that is received at location IIa picks up track relay TRN over a circuit that extends from rail 2 through conductors 66 and 12, the winding of relay TRN, conductor 13, back contact 14 of device TRP, conductor 63, back contacts 460 and 59-of devices KRN and KRP and conductor 62 back to rail I. During each of these pick-ups Contact 58 causes source TN to supply the rear section rails with a pulse of negative polarity master code energy. The supply circuit extends from the positive terminal of source TN through conductor 16, front contact 58 of relay TRN, back contact 51 of device TRP, conductor 10, the rear section rails 2ala, conductor 69, and impedance 68 back to the negative terminal of source TN. y

Each positive polarity pulse of feed back energy that is received from the rear section rails at location IIa picks up track relay KRP over a circuit extending from rail la through conductors 69 and 11, the winding of relay KRP, a back contact 18 of device KRN, conductor 19, back contacts 58 and 51 of devices TRN and TRP and conductor 10 back to rail 2a. During each of these pick-ups contact 59 causes source KP to supply the forward section rails with a pulse of positive polarity feed back energy. The supply circuit extends from the positive terminal of source KP through conductor 8l, front contact 59 of relay KRP, conductor 62, forward section rails l and 2, conductor 66, and impedance 89 back to the negative terminal of source TP.

Each negative polarity pulse of feed back energy that is received from the rear section rails at location IIa picks up track relay KRN over a circuit extending from rail 2a through conductor 10, back contacts 51 and 58 of devices TRP and TRN, conductor 19, a back contact 82 of device KRP, conductor 83, the winding of relay KRN and conductor 69 back to rail la. During each of these pick-ups contact causes source KN to supply the'forward section rails with a negative polarity pulse of feed back energy. The supply cirf In addition to.` repeating the coded energyfinv l the manner just describedthe: cut section facilities of Fig. 4, are capable of, repeating` steady energy of either positive or negative polarity and of either the master code-orthe feed back variety. Without4 interfering with the; complete system operation,v the Fig. 4: cut: section4 facilities may, therefore, be interposed between the entrance and exit ends I-I and EI. of the-coded feedback track circuit of either of Figs. 1 or 3.

cui section, facilities of Figs. 5 6,"

` Inv installations vwhere inductive "kick`back energy'y inl substantial `quantities is generatedv in the rails the just described apparatus of Fig. 4 may be replaced by one or the other ofthe cut section equipments ofFigs. 5 and 6. These two equipments safeguard their `relays against false response to kickback energy such asl has been described re reactors' 55 and? 56 of Figs. 1 andi 3f'.

The equipment of" Fig. 51 is'd'esigned` for use with coded' track circuitsof' the Fig. l'type wherein each received pulse of master codeL energy is followed by a supplied feed back pulse of opposing polarity; the equipment of Fig. 6 is designed for IIa interposed betweenl the entrance and exit lon cations of Fig. 1s signal block II--IIL Installed at this cut location are: (l)y av code following track relay I'Ra which has the same polar stickcharacteristics as does entrance endr device 'IR of Fig. 1 and which is operatedby master code energy pulses of both positive andnegative polarity that are received from Fig. 5s

L forward section rails I-2-; (2)- a repeater device Fig. 5 are: (l)` a po'sitive'source TP of masterf code energy which at proper times is connected withA the rear section rails ii- 2a. over conta-ctsf 86-81 of devices TRa-RPa; (2) a negative source TN of master code energy which at other; times is connected withthe rear section rails. over the same contacts; (3) a positive source KP of feed back energy which at properl times is connected'with the forward section rails I2 over contactsv 26 and 8-8 of devices RPa and KRa; and (4) a negative source KNof feed back energy which at other times is connected with the for-r ward section' rails over contacts 26 and 89 o f the just named devices. y

Each pulse of positive polarity master code energy that is received from the forward section I rails at Fig. 5s location IIa moves the contacts of4 track relay 'IRa' to thek left. Suchmovement. results from an energization. of.' that relayover apath,` from` railV I ythrough conductor' 92h the; winding of relay TRa, conductor 921,; back con-tact; 89 of` ydevice: KRa.;y and', conductor 93A back to rail. 2. During each .ofn `those left positioningsof-re'i-f lay- TRa.scontacts and before.repeater'RPafshifts its; contacts to the left, source TP supplies-,the, rear section rails with a pulse of positive polaritymaster .codez energy.l The: supply path extendsfromr the positive terminalofsource TP throughs f device- 'IRa-sg leftv contact 85; conductorv 9&1-,A the.; rear section railsI I 1f-20L,` conductor 95', a. current limiting impedance 96, conductor 91;, and de vice RPas right contact 81 back to thegnegative: terminal'of'sourceTP. A A n;

, Each forwardzsection pulse of negative.'polarity'vr master -code energy that isreceived at Fig-5s loi cation IIa movesthecontacts of track relay TRa; to the right. Such movement results from an.V energization ofy that relay over a path from rail. 21 through conductor93, deviceKR'as. ba'ckcon-f` tact. 88, conductorV` 92., the wi-ndingzof relay TR. and conductor 9| lback tofrail: I.r During. each of" those-right positionings of relay TRcLfsv contactsL and` beforerepeater RPa shifts its contacts to the right,isource/.TIN suppliesthe rear section rails with a pulse ofnegative polarity mast-encode eney ergy.' The supplypathextends fromA the positive` terminal. of source y TN, through device. RPas. left. contact, 8l, conductor' 9.1, impedance 9,6,.therear section.l rails ,Zar-Ia, conductorl 99 and. device; TRas right contact SG-.backto the. negative. ters-- minal ofsource .'lN.y v, I

Each positive polarity pulseof feedback ener-'f gy that is received' from.. Fig. 5s rear. section. rails at location IIa picks up track relay KR@ over a circuit.` extending from. rail I a through conductor 94,. device 'IRc'ts'f right. contact, I'l-iif,4 con` ductor 98 deviceA RPas, right contact. 9.9,. con.,` ductor l IUI), dev-ice 'I'Ra-sv rightcontact I`D..I,.'conf ductor I4, the winding of re1ay.KRa,conductor.. I5, device T'Ras right contact I92l,.conductor i113, and conductor back. torailvzc'. During each., of these pick-upscontact 88 causessource to. supply the. forwardsection railsv with a pulse. off

. positivevpolarity feed. backI energy. The supply path extends from the positive terminal of source KP through device. RPas righty contact 2.6,.a current limiting impedance. |96., conductorv 92` device. TRasA winding, conductor 9.I, the forward.Y sec; tion railsy I-Z, conductor 93,` and deviceKl-"tas` front. contact88 back tothe negative terminal of so'urceKl. n y v. v

Each negative polarity pulse. of feed; back. en..

ergy that is received from Fig. 5s-rear section; rails at location IIa also. picks up track relay KRa. Inthis case, however, the pick-up circuit. extends from rail Zathrough conductor 95,. con..- ductors Illa-|94, device 'I'Ras left contact I''I,. conductor I4, the winding. ofrelay KRa;,. conductor. I5,.d evice T-Ras left contact I 02conduc-- tor I 90, device `RPaLs left contact 99,y conductor,

1.05device TRas. left contact 86,. and conductorl 9,4 back: to raid.v Ia. During, each, of' these. pick.-` ups contact 89 causes source KN to supply the forwardt sectionY rails with. a..pu1se-of negative. pol larity feed back energy. 'Ihe supply pathextends fromf the positive terminal of source KN through). device-KRas frontcontact- 89, conductor. 93;,theforward section. rails 2-I, conductor 91,. device:

. g-TRaswinding, conductor 92, impedance |06, and-l device RPaslleft contact 26 backto thenegative. terminalof source KN. I

'The fjust' examined cut sectionfacilitiesy of Fig, 5` thus are.v eiective,v to repeatboth master code? and fff'eed: back. energy pulses; of both. polaritiesfand they may, therefore, be interposed between the entrance and exit ends II and III of Fig. ls coded track circuit Without in any way interfering with that circuits operation.

When rail kick back energy of the character earlier described is encountered in objectionable magnitude Fig. s basic code repeating combination may be supplementted by a reactor which prevents detector track relayKRa from faselY responding to such energy under shunted conditions of the rear section rails. As in the case of Fig. ls similarly designated element, this reactor 55 is organized as per my copending application for Letters Patent of the United States Serial No. 455,170 and it keeps relay KRas winding connected with rails la-2a at and following the end of each master code energy pulse.

Such connection causes each pulse of master code energy that is applied to rails la-2a by sources TP-TN to flow unidirectional current through the winding of relay KRa.. Thus, source TP flows current through thatwinding over a path which includes device TRas left contact 85, reactor 55, device TRas left contact H12, conductor i5, the winding KRa, conductor i4, device 'IRas left contact IDI, conductors |04- I03, impedance 96, conductor 91, and device RPas right contact 8l; likewise, source TN flows current through the same winding over a path which includes device RPas left contact 81, conductor 91, impedance 96, conductor |03, device TRas right contact |02, conductor l5, the winding of KRa., conductor H, device TRas right contact IUI', reactor 55, and device TRas right contact 86.

In both instances the direction of this current flow through relay KRas winding is from right to left and in consequence relay KRa is heldreleased for the duration of each supplied master code energy pulse.

In addition this right to left owing current renders relay KRa immune to false pick-up by master code kick back energy which may be applied thereto following each disconnection of sources TP-TN from the rear section rails I a-2a.

Upon each of those disconnections: (l) rails I a-2a tend to flow through the winding of relay KRa, a master code "kick back current in the direction of from left to right; and (2) the energy of self-inductance in relay KRas winding plus that in reactor 55 tends to continue the flow therethrough of current in the opposite or right to left direction.

. These currents directly oppose each other and by choosing the magnitude of the windings plus reactors kick back current to slightly exceed that generated in the rails, relay KRa, is effectively held released following each disconnection of master codesources TP-TN from rails Ia-2a.

In the case of Figs 5s master code track relay 'I'Ra, no kick back neutralizing reactor is needed and hence none has been shown. Like device TR of Fig. l, this track relay TRa utilizes the kick back safeguarding expedients of assignees United States Patent 2,286,002 to Nicholson. Trackway current originating in each of Fig. 5s feed back sources KP-KN passes in series through the winding of relay TRa in such direction as to hold that relays contacts in the position to which they were moved by the pulse of master code energy last received frorn'rails I-2. As kick back current from those rails flows in the same direction through the relay winding it cannot produce false operation of relay TRa and hence no neutralizing reactor is needed therefor.

Referring now to Fig. 6, I have there shown cut section apparatus which is generally equivalent to that of Fig. 5 but which differs therefrom by being designed for use with track circuits of the Fig. 3 'type wherein each received pulse. of master code energy is followed by a supplied feedi back pulse of the same polarity.

Like Fig. 5, the apparatus of Fig. 6 includes: (l) a first code following track relay TRa of the polar stick type which is operated by "master code energy pulses of both positive and negative polarity that are received from the forward section rails |-`2; (2) a repeater device RPa for that master track relay TRa; and (3) a second code following track relay KRa. of the polar biased type which is operated by feed back energy pulses of both positive and negative polarity that are received from the rear section rails lez-2a.

Like Fig. 5 also, the apparatus of Fig. 6 further utilizes: (1) positive and negative polarity sources TP and TN for supplying master code energy to the rear section rails la--2a;A and (2) positive and negative polarity sources KP and KN for supplying feed back energy to the forward section rails 1 2.

In operation of this Fig. 6 apparatus, each pulse of positive polarity master code energy that is received from the forward section rails at location IIa moves the contacts of track relay TRa to the left. Such movement results from an energization of that relay over a path from rail I through conductor 9i, the winding of relay Tlta, conductor H38, aback contact |09 of device KRa, and conductor 93 back to rail 2.

During each of these leftpositionings of relay TRas contacts and before repeater RPa shifts its contacts to the left, source TP supplies the rear section rails with a pulse of positive polarity master code energy. This supply is from the positive terminal vof source TP, through device TRas left contact 8E, conductor 94, the rear section rails Ia-2a, conductor 95, impedance 96, conductor 91 and device RPas right contact 81 back to the negative terminal of source TP.

Each forward section pulse of negative polarity master code energy that is received at Fig. 6s lo cation IIa moves the contacts of track relay TRa to the right. Such movement results from an energization of that relay over a path from rail 2, through conductor 93, device KRas back contact |09, conductor |03, the winding of relay TRo'., and conductor 9i back to rail I. During each of those right positionings of relay TRas contacts and before repeater RPa shifts its contacts to the right, source TN supplies the rear section rails with a pulse of negative polarity master code energy. This supply is from the positive terminal of source TN, through device RPas left contact 81,' conductor 9'1,y impedance 9B, conductor 95, the rear section rails 2li-la, conductor 94. and device TRas right contact 86 back to the negative terminal of source TN.

Each positive polaritypulse of feed back energy that is received from Fig. 6s rear section rails at location IIa picks up track4 relay KRa over a circuit from rail la through conductor 94, device 'IRcs left contact |92, conductor H5, the winding of relay KRa, conductor i 4, device TRas left contact |01, conductors IEM-|03 and conductor back to rail 2a. During each of these pickups contact 89 causes source KP to supply the forward sectionfrail'sA with a pulse of positive polarity feedi back: energy. Thewsupply path ex'- tends' from. the Apositive terminal of source KP, through device EPas left contact 26,' conductors 92-BI, the forward section rails I,-2, conductorA 93; device KRasv front contact 89',r and a. current limiting impedance l I ly backl to the negative terminal of source Each negativei polarity pulse of feed` backenergy that isy received from Fig.` 6s rear .section rails` also picksiup. track relay KRa. vat location IIa.. Infthisfcase, however, the pick-up circuit extends from rail l2a`through conductors B5 and H13; device TRas rightcontact 'm2, conductorlz5, the winding'of relay KRa; conductor |11, def vice .'I'Ras rightzcontactI mgl; and conductor 94 back to rail` la. During each of these pick-ups contact 88 causes source KN to supply the forf the entrance and exit ends II: and III of'Fig;-3s

coded track` circuit Without'in any ing with that circuits operation.

When rail kick back' ofthe character earlier described'isv encountered in objectionable magwayl interfernitude, Fig.' sbasic code-repeating combination I! maybe supplemented by a reactor56 which prevents master track relay TRa from falsely. lresponding to'such energy 'under shunted condi'- tions of the forwardv section rails. As in the case ofFig. 3s similarly designated element, this re- 1 actor 56 is organized asper my copendingA applifcation for Letters-r P'at'e'nt of the United States v Serial No. 455,170 and itA keeps relayTRaswinding' connected with rails I--Zv at and' following .A

'the end of each feed baok'energypulse. I

Such connection causes each pulse ofvfeed back I energy that is' applied to` rails I'-2' by sources ,KP- KN to flow' unidirectionalfcurrent through Yvided therefor;

iiftendsftocontinue. the flow therethrough of current in theopposite or leftto righi, direction.v The-latter current may be chosen to overcome the former and following each disconnection of feed backsource KP from the forward section rails; it then holds relay 'IRas contacts tothe left'I f Upon each such disconnection of, the negative feedback source KN: (11 rails l,-2` tend to ow through thewinding of relay TRa, a trackway kick back current in the 'direction of from left to.` right; and :(21)` the energy of self-inductance in relay.TRas'vi/indingv plus that in vreactor 56 tendstocontinuethe flow therethrough Yof current; in the oppositel or right to left direction. The latter current may be chosen to overcome the former andfollowing each disconnection of feed back source KN from the forward section .rails` it' thenholds" relay TRas contacts tothe right. Y

In the case vof Fig. 6s feedback detector relay .KRzn no kick back neutralizing` reactor is needed: andihence none has been' shown. Like device; KRI` 0f Fig. 3, this detector relay-forms part of -al combination which is inherentlyjself'- 'protecting against-false relay operation by kick back energyy that-.may be impressed thereon from r-ails.:"'la2a. I k: f v Ink thetrack circuit of Fig. 3 with whichthe Fig; 6 cut', section equipment isV designed to be used,v each entrance-end receivedpulse of master code energy is: followed by a feed back pulse of the samev polarity and relay KRa of Fig; 6v thus is the counterpart of Fig. 3s vrelayKltl. The reasonswhy the latter cannottfalsely be operated by. rail kick back' energy have already been examined'in detail. Those same reasons vapply'to relay KRu vof Fig. 6 and hence no reactor cor-` respondingl to Fig. lvs element.` 55 need be pro- .Summary From the foregoing it will be seen that the improved "coded feedback-track circuitsk of my invention are of broad utility and that their applicationis by nomeans-restricted to the apthe winding'ofrelayi'I'Pua.' Thus', source KP flows preach Ilighting uses which are herein shown by Way of illustration.` While,'moreover, the approach controlfacilitiesof Figs-1 and 3 have beenexplained in polar impulse systems whereinthe lights of wayside-'signals only are appreach governed, it` will be understood that these facilities haveequalutility when used with 93; device KRas front' contact Biiand impedance l I"|"I. Such current keeps relay TRas contacts to thel'eft. i

Source KN also owscurrent through relay 'I'Ras winding but in the direction of' from right toy left. This flow is over device KRas Afront contact 88, conductor 93,' reactory 515,` thewinding of relay. TRa, conductor 92' vand'device RPas' right contact 2li. By i't relay I'Ras contacts are'kept tothe-right. f

In each instance'ths feed backr 1:roducedcur'` I rentA flow: renders relay TRa immune to false 'operation by rail kick back. energy which may be applied thereto followingeach disconnection of 'feed back sources KP-KN,from the forward section rails |-2'.

Upon each such disconnection of the positive feed back source KP: (1) rai-ls l`-'2 tend. to ow through the windingnof relay IRa a trackway -kick back current inV the direction offrom right to left; and (2') the energy of self-inductapproachl vcontrol combinations which provide for other comparable functions instead of or in addition to theillustrative one here illustrated. .Byv thesefimproved .-coded feedbacktrack circuits a. number of vimportant advantages are offered and Ato f these-'attention will now vbe directed., Y

, Eirst,- the master code operating advantages 0f my issued' United States. Patent No. 2,282,0995

vpolar impulse4 coded control circuits are im,-

- these operating advantages include a lowering` of powerV requirements: plus 'further desirable features. 1 l.

Second,` both` the' feed `bacia-andv the master code relays KR and TR of the circuitA are rendered; highly :immune to false operationr yby lforeign currents thatA may be present in the circuit conductors. Each of the named relays can be operated only.v by' energy in the 'track 'rails moe in relay TRas winding plus'that in reactor 75 which isy of DeriOdCally `rei/@P8601 'Polarity (See Fig. 2). Unless foreign current present in the rails is of that special character it, quite obviously, cannot produce false relay operation.

Third, storage energy difficulties are eliminated to a greater extent than has been possible in the past. Energy stored in the track ballast and rails following each application of code pulse energy (either master or feed back) thereto retains the polarity of the applied pulse and the potential thereof can progressively build up only when successive applied pulses are of the same polarity. By my alternate reversals of both master code and feed back pulse polarity (once more see Fig. 2) I keep the level of storage potential far below that which is effective for producing false operation by either the master code track relay TR or by the feed back detector relay KR.

Fourth,l both the feed back detector and the vmaster code track relays KR and TR are rendered immune to false operation by kick back energy that may be present in the rails. Depending upon the circuit details this immunity is achieved: v(l) by the series relay expedients of United States Patent No. 2,286,002 to Nicholson, as for device TR of Fig. 1 and device TRa of Fig. 5; (2) by the neutralizing reactor expedients of my copending application for Letters Patent of the United States Serial No. 455,170, as for device KR of Fig. 1, device TR of Fig. 3, device KRa of Fig. 5, and device TRa of Fig. 6; and (3) by the inherently self-protecting organization of this invention, as for device KRI vof Fig. 3 and device KRa of Fig. 6.

In addition to thus improving the operating characteristics of coded feed back control circuits per se, I have provided improved facilities for impressing the pulsed feed back energy upon the circuit conductors and for receiving that energy from those conductors; and I have organized the improved facilities in such manner that the resulting coded feed back control circuits are readily usable in signaling systems of the frequency code and other types of commercially proven practicability.

Although the several improvements of my invention have been shown and described as forming part of coded feed back control circuits of the track type, it will be obvious that these improvements are not restricted thereto but that they also have utility when applied to control circuit combinations of any other form wherein the conductors lose their normal energy transmitting capability under certain conditions only.

Thus, instead of being track rails as shown, the control circuit conductors i--2 may also take the form of line wires which connect master energy supply and feed back receivingequipment (see devices CR-CP-KR at location III in Figs. l and 3) at one end of the circuit with master energy receiving and feed back supplyl equipment (see devices TR/-RP--KP-KN at location II in Figs. land 3) at the other end of the circuit.

When used in a control circuit of the line conductor type just described, each of the improvements herein disclosed will function in exactly the same manner as when used with the track type of control circuit that is herein illustrated. My invention is, therefore, one of broad utility and is not to be restricted to the specific forms of application that` I have shown by way'of illustration.

Although I have herein shown and described only three forms of coded feed back control circuits embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination, a control circuit that includes a pair of conductors which normally are capable of transmitting energy between given and opposite ends of the circuit but which at times are rendered incapable of such transmission, mean sincluding a coding device at the given end of said circuit for supplying said conductors with master code energy in the form of recurring on period pulses that are separated by off period intervals and that have positive and negative polarities in alternating sequence, a first code following relay at the opposite end of said circuit connected with said conductors during said master code on periods and having a contact which moves to a normal position upon each reception of a positive polarity masterv code pulse and to a reverse position upon each reception of a negative polarity master code pulse, means governed by said rst relay contact and effective during code following operation thereof for'further supplying said conductor with feed back energy in the form of pulses that recur in step with said master code off periods and that have positive and negative polarities in alternating sequence, a second code following relay at said given circuit end having an operating winding and being provided with a contact which picks up when given direction current is passed through said winding but which stays released when that winding receives opposite direction current or no current at all, means governed by said coding device for establishing from said conductors to said second relay winding a connection which is direct during each master code off period of odd number and reversed during each master code off period of even number and over which each conductor-transmitted pulse of said positive polarity feed back energy and of said negative polarity feed back energy iiows given direction current through said second relay winding and thereby picks up said second relay contact, and apparatus controlled by said second relay contact and distinctively responsive according as that contact is or is not being repeatedly shifted between its said picked up and released positions.

2. In combination, a control circuit that includes a pair of conductors which normally are capable of transmitting energy between given and opposite ends of the circuit but which at times are rendered incapable of such transmission, positive and negative sources of master code energy at the given end of said circuit, a coding device which repeatedly connects said .circuit conductors first to said positive source and then to said negative source and thereby produces a master code made up of recurring energy pulses which have positive and negative polarities in alternating sequence, a repeater relay for said coding device which interrupts each of said conductor-to-source connections early in the code period that the connection defines and which thereby causes each of said master code pulses to be followed by an o period interval, means located at the opposite end of said circuit and operated by the there received received pulses of said master code energy for further supplying said conductors with pulses of feed back energy that accoglie recur in step with .said master code off periods and that have positive andnegative polarities in alternating' sequence, a code followingfrdetector relay at said given circuit end having an operatp ing winding and being provided with :a contact which picksup when given directioncurrenft is passed through said winding but which stays 1released when that winding receives opposite direction current or no current at all, connections jointly controlled by said kcoding device and by" vsaid positive polarity master code energy and of said negative polarity master code energy `flows opposite direction current through said relay winding and thereby is ineffective for picking up said relay winding, and apparatus controlled by said detector relay contact and distinctively responsive according asthat Contact is or is not conductor-supplied pulse of said positive 'polarity .master codeenergy'and of said negative polarity master code energy rows opposite rdire'ction currentgthrough ysaid detector relay winding and thereby. :is -vineffective 'for picking up said `det'ec tor lrelay contact, and apparatus controlled 'by vsaid detector relay contact and distinctively 1relspunsive :according as `that 'Contact `is or .is 'not being .repeatedly shifted between .its `said picked up and released positions.

4. Inlfcombination, Va controlcircuit that .ini -cludes a Apair of `conductors which normally are capable of transmitting energy between given and .opposite-ends of the circuit but which at times are rendered incapableof .such Ytransmis-- sion, positive far-rd 'negative .sources of 'master code energy fat the given .end -of .said circuit, la

' coding device having .a contact 4`which .repeatedly connects said circuit conductorsv first to said positive-source and then to said negative source and f thereby produces'a master .code made up of :re-

being repeatedly shifted between its said picked`v up and released positions. f

3. In combination, Aa control circuit that includes a `pair of conductors which normallyare capable of transmitting energy between given and opposite ends of the circuit but which `at vtimes are rendered incapable :of such transmission,

positive and negative sources of master code `energy at the given end of saidpcircuit, a coding device having a rst contact which repeatedly connects said circuit conductors iirst to said vpositive source and then to said negative source and thereby produces a master code made up o-f recurring energy pulses which have positive and negative polarities in alternating sequencega r`e,' peater relay for said codingdevice havingra con.-`

tact which interrupts each offsaid 4conductor-tosource connections early inthe code period that lthe connection defines and which thereby causes each of said master code pulses to be followed by an "off period interval, means located at the opposite end of` said circuit and operated by the there received pulses of said master code ener-gy for further supplying'said conductors with pulses of feed back energy that recur in step with .said master code off periods and `that have positive and negative polarities in alternating sequence,

a code following detector relay at said given circuit end having an operating winding and being providedwith a contact which picks up when given direction current is passed through .said

winding but which stays released when that winding receives opposite direction current or .no current at all, secondand third contacts of said coding device which operate in synchronous relation with respect to that relays said first contact and which in cooperation with said repeater rel lay contact bridge said `detector relay winding directly across said circuit conductors during curring pulses which have positive and :negative polarities in 'alternating'sequenca 'a repeater jrelay for `said coding `-.device .having 'a Vfirst `contact which interrupts Ieach rof said `conductor-'toysource connections early in the code period that .the connection defines and which ythereby causes each'of lsaid master Vcode pulses to be `followed 'by an off period interval, means located at theopyhesite "end yof said circuit and operated :by the lthere .received pulses of said master code energy for tur-ther supplying said conductors'with pulses of'feed backk energy that recur in :step with said master code off periods and that have positive and negative polarities in alternating sequence, a code following vdetector relay at said given cir cuit end having an operating winding and being provided with a contact which picks upwhen given direction current .is passed through 'said winding but which stays released when `that winding receives oppositev ldirection lcurrent `or no current yat all, second and third contacts Iof said repeater relay which `operate in synchronous relation with respect vto that relays said :first contact and which in cooperation with said cod'- ing device contact bridge said detector relay Winding directly across vsaid circuit conductors during master code off periodsi'of odd number and reversely across said conductors during master code off periodsof even number Iwhereby each conductor-transmitted pulse of said positive polarity feed back energyand of saidy negative polarity feed back energy .flows given direction current through said winding and thereby picks up said detector relay conta-ct and whereby each conductor-:supplied pulse of said positive polarity master code energy and of saidnegative polarity master code energy .iiows opposite vdirec-tion lcurrentfthrough said detector relay winding and thereby is ineffective for picking up said detector -relay contact, and apparatus controlled -bysaid vdetector relay contact and distinctively responsive according :as Vthat contact is 'vor is not being' .repeatedly shifted between its said picked up 4and released positions. y

f5. In combination, a control circuit lthat includes a pair of conductors `whiclfrnormally. are* capable of transmitting energy between given and opposite ends of the circuit but which at ytimes 'are 'rendered incapable of such transmission, means -at the -given end of said circuit :for

supplying said conductors with master code energy in the formof recurringon'" period pulses that are separated by foiT'period intervals and 'that have positive and negative polarities inra-1^- .7"

which is connected with said conductors and be- ;ing provided with a contactv which responds to each winding-received pulse of said positive po- -larity master code energy by moving to a first position and which responds to each winding-received pulse of said negative polarity master code ,energy by moving to a second position, positive 'pulse of negative feed back energy upon those conductors, means also including said relay contact but effective upon each of said second positionings thereof for connecting said positive source with said circuit conductors by way of said relay winding and in such manner as to pass through the winding current that continues said contact in said second position and -that impresses a pulse of positive feed back energy upon those conductors, a repeater device for said relay vwhich interrupts each of said feed back supply Yconnections before the end of the master code off period during which that connection occurs, and apparatus at said circuits given end .controlled by the said polarized feed back pulses which are there received and selectively responsive according as said reception does or ldoes not take pla-ce.

6. In combination, a control circuit that includes a pair of conductors which normally are capable of transmitting energy between given and opposite ends of the circuit but which at Atimes are rendered incapable of such transmission, means at the given end of said circuit for.

supplying said conductors with master code en- :ergy lin the form of recurring on period pulses :that are separated by olf period intervals and that have positive and'negative polarities in al- 'ternating sequence, a code following relay at the .opposite end of said circuit having a winding which is connected with said conductors and being provided with a contact which responds to each winding-received pulse of said positive polarity master code energy by moving vto a first position and which responds to each windingreceived pulse of said negative polarity master code energy by moving to a second position, positive and negative sources of feed back energy at said opposite circuit end, means including said relay. contact and effective upon each of said first positionings thereof for connecting said negative source with said circuit conductors by Way of said winding and. in such manner as to lpass through the winding current that continues said contact in said first position and that' impresses a pulse of negative feed back energy upon those conductors, means also including said relay contact but effective upon each of said second positionin'gs thereof for connecting said positive -source with said circuit conductors by way of said -ternating sequence, a code following relay at the opposite end of said circuit having a Winding curs, a contact of said repeater device which upon each of said feed back supply interruptions connects said relay winding in direct energy receiving relation with said circuit conductors,A and apparatus at said circuits given end controlled by the said polarized feed back pulses which are there received and selectively responsive according as said reception does or does not take place.

7. In combination, a control circuit that includes a pair of conductors which normally are capable of transmitting energy between given and opposite ends of the circuit but which at times are rendered incapable of such transmission, means at the given end of said circuit for supplying said conductors with master code energy in the form of recurring on period pulses that are separated by off period intervals and that have positive and negative polarities in alternating sequence, a code following relay at the opposite end of said circuit having a winding which -is connected with said conductors and being provided with a contact which responds to each winding-received pulse of said positive polarity master code energy by moving to a iirst position and which responds to each winding-received pulse of said negative polarity master code energy by moving to a second position, positive and negative sources of feed back energy at said opposite circuit and, means including said relay contact and effective upon each of said first positionings thereof` for connecting said positive source with said circuit conductors whereby to supply them with a pulse of positive feed back energy that continues said contact in said rst position, means alsoincluding said relay contact but effective upon each cf said second positionings thereof for connecting said negative source with said circuit conductors whereby to supply them with a pulse of negative feed back energy that continues said contact in said second position, a repeater device for said relay which interrupts each of said feed back supply connections before the end of the master code off period `during which that connection occurs, and apparatus at said circuits given end controlled by the said polarized feed back 4pulses which are there received and selectively responsive according as said reception does on does not take place.

8. In combination, a section of railway track, means including a coding device at the exit end of said section for supplying the section rails with master code energy in the form of recurring pulses that are separated by 01T period intervals, means located at the entrance end of said section and operated by the there received pulses of said master code energy for further supplying said conductors with pulses of feed back energy that recur in step with said master code off periods and that have positive and negative polarities in alternating sequence, a code following detector relay at said sections exit end having an operating winding and being provided with a contact which picks up when given-direction current is passed through said winding but which stays released when that Winding receives opposite direction current or no current at all, means governed by said coding device for establishing from said rails to said detector relay winding a connection which is direct during each master code off period of odd number and reversed during each master code "ofF period of even number and over which each conductor-transmitted pulse of said positive polarity feed back energy and of said negative polarity feed back energy flows in said given-direction current through said relay winding and thereby picks up said relay contact, and apparatuscontrolled by said detector relay contact and distinctively responsive according as that contact is or is not being repeatedly shifted between its said picked up and released positions.

9. In combination, a stretch of railway track arranged into rst and second sections that adjoin at a common point, means at the remote end of said second section for supplying the second section rails with master code energy in the form of recurring pulses that are separated by off period intervals and that have positive and negative polarities in alternating sequence, means at the said point of section junction for repeat- Aing into the rails of said first section each pulse of said master code energy that is received at that junction point and lfor coinciding the polarity ci each repeated pulse with that of the received pulse by which it is produced, means located at the remote end of said first section and controlled by the said repeated pulses of master code energy that are there received for further supplying said rst section rails with recurring pulses of feed back energy that coincide with the off period intervals of i' said repeated mastercode and that have :positive an'd negative polarities in alternating sequence, further meansl at the `said point of section junction for repeating into said second section rails during the off period intervals of said second section master code the pulses of said feed back Aenergy that are there received from said first section rails and for coinciding the polarity of each repeated pulse with that of the received pulse ley-,Which it is. produced, and apparatus controlled by said re-` peated reed back pulses and distinctively responsive according as those pulses are or are not bcingreceived at the remote end of said second section.

10. In a coded track ycircuit signalling system for railroads, a section of railway track, means for applying to the rails at one end of the sec-l 11. In a coded `track circuit signalling system for railroads,` a code transmitting and receiving means comprising, a code following track relay, a source of energy, a transmitting relay operable to its opposite positions at any desired code rate, a two position polarized timing relay, circuit means for operating said timing relay to an opposite position upon each operation of said transmitting relay to an opposite position, and means 1Q including contacts of said transmitting relay and said timing relay to normally connect said track relay across the rails of a track section but acting upon each operation of said transmitting relay to disconnect said track relay from said railsA and momentarily connect said source across said rails until said timing relay is operated.

l2. In combination, a stretch of railway track arranged into first and secon-d sections that adjoin at a common point, means at the remote end of said second section for supplying the second section rails with master code energy in the form of recurringv pulses that are separated by off period intervals and that have positive and negative polarities in alternating sequence, meansat the said :point of section junction for repeating into the rails of said rst section each lpulse of said master code energy that is received at `that junction point and for causing said repeated pulses to have positive and negative polarities in alternating sequence, means located at the remote end of said first section and controlled by the said repeated pulses of master code energy that are there received for further supplying said rst section rails with recurring pulses of -feed back energy that coincide with the off periodintervals of said repeated master code and that have positive and negative polarities in a1- ternating sequence, further means at the said point of section junction for repeating into said tervalsof said second section master code the [pulses of said feed fback energy that. are there received from said rst section rails and for causing said repeated pulses to have positive and negative polarities in alternating sequence, and apparatus controlled by said repeated. feed back pulses and distinctively responsive according to those pulses are or are not beingreceived at o the vremote end of said second section.

HOWARD A. THOMPSON.

second section rails during the .oif period in-` 

